The manufacture of semiconductor devices is a complex process that can involve over 200 process steps. Each step requires optimal conditions to ultimately result in a high yield of semiconductor devices. Many process steps require the use of fluids to inter alia etch, clean, expose, coat, and polish the surface layers of the devices during manufacturing. In high purity fluid applications, the fluids (e.g. hydrofluoric acid, sulfuric acid, ammonium hydroxide, hydrogen peroxide, etc.) must be substantially free of particulate and metal contaminants in order to prevent defects in the finished devices. In chemical-mechanical polishing slurry applications, the slurries (e.g. Semi-Sperse®-12, iCue® 5001, Klebosole® 1501, Cab-O-Sperse® SC-112, etc.) must be free from large particles capable of scratching the surfaces of the devices. Moreover, during manufacturing there must be a stable and sufficient supply of the fluids to the process tools carrying out the various steps to minimize process variability and manufacturing downtime.
As semiconductor manufacturers design new devices in-line with the International Technology Roadmap for Semiconductors (ITRS) to produce smaller, faster and more reliable devices, new manufacturing challenges arise. Solutions to these challenges often require the use of novel or non-traditional fluids in the manufacturing process. An example of such a challenge is electromigration in copper interconnects. Electromigration occurs when electrons push and move the metal atoms in the direction of current flow at a rate determined by the current density. Electromigration can lead to thinning of the interconnect, high resistivity, or a line break. (see P. Singer, “The Advantages of Capping Copper with Cobalt,” Semiconductor International, October 2005).
There are two known methods for eliminating electromigration in copper interconnects. One method is to form a cap on the interconnect by first depositing a palladium activation layer over the surface of the copper and then introducing an electroless cobalt solution to react with the palladium and form an electroless cobalt tungsten phosphide (CoWP) layer on the palladium. Another method is to use a self-activating process, which would not require deposition of palladium. In this process, a complex and unstable deposition fluid containing inter alia cobalt and acid is applied directly to the copper to form a cobalt cap layer on the copper. (see P. Singer, “The Advantages of Capping Copper with Cobalt,” Semiconductor International, October 2005). While these processes show promise to solve the problem of electromigration in copper interconnects, the cobalt solutions they employ are expensive particularly when such solutions are discarded after every use.
Semiconductor manufacturers historically have been reluctant to reclaim and recycle semiconductor process fluids primarily due to concern of contamination in the recycled fluids resulting from particles, metals and/or degradation of the fluid. Moreover, some fluids require a complex series of operations to be performed (e.g. distillation, adsorption, carbon filtration, etc.) before they are ready for reuse by a semiconductor tool. It may be that reclaim and recycle equipment costs and potential manufacturing downtime resulting from out of spec recycled fluid, have outweighed the gain of reclaiming and recycling the process fluids. However, with the emerging use of costly non-traditional solutions (e.g. the cobalt solutions mentioned above), there is a need for methods and apparatus for reclaiming and recycling semiconductor process fluids.